1. Field of the Invention
The present invention relates to a balance shaft housing, and more particularly to a housing for accommodating balance shafts provided with counterweights for canceling out the vibromotive force caused by pistons.
2. Description of the Related Art
For example, JP-B-5-39233U discloses a balancing device in which balance shafts provided with counterweights for canceling out the secondary vibromotive force generated by pistons of an engine are disposed below a crankshaft within an oil pan and in which the rotation of the crankshaft is transmitted to the balance shafts via a chain/sprocket mechanism or a gear mechanism.
With this balancing device, if the balance shafts vibrate, the damping effect deteriorates. Therefore, the housing for rotatably supporting the balance shafts needs as high rigidity as possible.
However, if the thickness of the whole housing is increased in order to increase the rigidity of the housing, the housing would need to be enlarged. This modification detracts from the goal of reducing the weight of the engine.
The invention was made to solve the problem inherent in the related art, and a primary object thereof is to provide a balance shaft housing which is constructed so as to increase the rigidity thereof without causing a weight increase or complicated construction.
In view of the above object, according to the invention, there is provided a balance shaft housing (an upper housing 14U and a lower housing 14L) disposed in an oil pan (7) for accommodating balance shafts (13L, 13R) provided with counterweights (19) for canceling out the vibromotive force caused by the pistons, wherein an intake passage (an intake pipe 32) of a pump (27) for receiving lubricating oil within the oil pan is formed integrally with the housing, and an oill strainer attaching portion (34) is formed integrally with a bearing wall (a first bearing wall 26) for supporting the balance shafts.
According to this construction, since the thickness of the oil strainer attaching portion helps increase the rigidity of the bearing wall supporting the balance shafts, the increase in rigidity of the housing can be attained without increasing the thickness of the housing. Moreover, since the oil strainer is attached directly to the housing, it can help make the engine compact.
In particular, the intake passage and the oil strainer attaching portion are formed continuously along axes of the balance shafts, and a plurality of bearing walls for supporting the balance shafts are connected to each other by the intake passage and the oil strainer attaching portion. According to this construction, the rigidity at the bearing portions can increase further.